Cell station, radio communication system, communication control method of cell station, and method of building radio communication network

ABSTRACT

Traffic that can be processed at a cell station is increased without reducing communication quality. When a channel is allocated to every time slot constituting a communication frame and radio control section receives a link channel establishment request from a personal station through a control channel allocated to any of the time slots, a control section notifies the personal station through the traffic channel of an allocation message indicating that the time slot allocated to the control channel will be allocated to a traffic channel. The transmission of the control channel is stopped when a predetermined time (a control channel transmission/reception duration) passes after the notification of the allocation message.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a communication control technique and, more particularly, a technique for accommodating personal stations by using the time division multiple access method.

[0002] For example, one communication control technique for accommodating personal stations by using the time division multiple access method is the personal handyphone system defined in “Second Generation Cordless Telephone system RCR STD-28”, issued by Research & Development Center for Radio System. Japanese Patent Laid-Open Publication No. H10-136438 (hereinafter referred to as Patent Document 1) is disclosed a technique for accommodating a greater number of personal stations in such a radio communication system using the time division multiple access method.

[0003] Referring to Patent Document 1, in the case that, when a channel is allocated to every time slot constituting frames transmitted and received, a cell station receives a link channel establishment request from a personal station through a control channel allocated to any time slot when a channel is allocated to every time slot constituting frames transmitted and received, the cell station stops transmission of the control channel and allocates a time slot which has been allocated to the control channel to a traffic channel. Thus, a greater number of personal stations are accommodated.

[0004] Referring again to Patent Document 1, before a cell station starts the service, the cell station checks from an identifier set for itself whether the cell station can operate in both of a first mode in which a control channel is always allocated to any time slot constituting a frame and a second mode in which traffic channels can be allocated to all of time slots constituting a frame. When it can operate in both modes, the cell station obtains identifiers informed from other cell stations located in the neighborhood and checks whether there is any cell station operating only in the first mode among those cell stations. The cell station sets itself for operations in the second mode only when such a cell station exists and sets itself for operations in the first mode when no such cell station exists. Such an arrangement prevents a situation wherein all cell stations belonging to the same service area stop transmission over the control channel and personal stations in a ready state are handled as location being outside the area.

SUMMARY OF THE INVENTION

[0005] However, the technique disclosed in Patent Document 1 has the following problems.

[0006] Let us assume that a time slot for a control channel is allocated to a traffic channel of a certain personal station. In the case that the personal station cannot recognize the allocated traffic channel as a result of carrier sensing, the personal station transmits a re-request for allocation to the cell station. However, according to the technique disclosed in Patent Document 1, the re-request for allocation cannot be received because the cell station has already stopped transmission and reception of the control channel. As a result, the personal station continues transmitting the re-request for allocation until the personal station becomes in a ready state for another cell station, and a call to the personal station may not be connected.

[0007] Let us assume that, in the case that time slots constituting a frame which have been allocated to respective traffic channels at a cell station, a call is terminated and an open slot is produced. In this case, carrier sensing for the control channel is performed in the open slot, and the control channel is allocated to the open slot after it is confirmed that there is no interference. However, when a plurality of cell stations in the same service area perform such an allocating process, a plurality of cell stations can transmit and receive the control channel at close timing. In this case, interference can be detected during the carrier sensing for the control channel because of time lags in transmitting and receiving the time slot attributable to an error in the operating clock of each of the cell stations, and the control channel may not be allocated to the open slot. This results in call loss and a reduction in the traffic. No consideration to such a situation is reflected in the technique disclosed in Patent Document 1.

[0008] Before starting a service, the cell station decides a mode of operation, i.e., a first mode in which a control channel is always allocated to any of time slots that constitute a frame or a second mode in which a traffic channel can be allocated to every time slot constituting a frame. However, the mode of operation decided prior to the operation may not be appropriate for an actual traffic. No consideration to this point is reflected in the technique disclosed in Patent Document 1.

[0009] The present invention is made taking the above-described situations into consideration, and it is an object of the present invention to improve the traffic that can be processed at a cell station without any reduction in communication quality.

[0010] In order to solve the above-described problems, in a first aspect of a cell station according to the present invention, when a time slot for a control channel is allocated to a traffic channel of a certain personal station and the personal station cannot recognize the allocated traffic channel, the cell station can receive a re-request for allocation transmitted by the personal station.

[0011] For example, a cell station in this aspect of the present invention is a cell station accommodating a personal station by using a time division multiple access method including communication unit which transmits and receives a frame including a plurality of time slots and control unit which allocates a traffic channel or a control channel to each of the time slots constituting the frame. In the case that a channel is allocated to every time slot constituting the frame, when the communication unit receives a link channel establishment request from the personal station through the control channel allocated to any of the time slots, the control unit notifies the personal station through the control channel that the time slot allocated to the control channel will be allocated to a traffic channel and stops transmission and reception of the control channel when a predetermined time passes after the notice.

[0012] In a second aspect of a cell station according to the present invention, when a time slot which has been allocated to a traffic channel is to be allocated to a control channel, the control channel is allocated to the time slot at timing for transmitting and receiving a frame including the control channel which has been registered in advance. The frame transmission/reception timing registered in advance is timing at which no interference has been detected as a result of carrier sensing for the control channel.

[0013] For example, a cell station in this aspect of the present invention is a cell station accommodating a personal station by using a time division multiple access method, including communication unit which transmits and receives a frame including a plurality of time slots, control unit which allocates a traffic channel or a control channel to each of the time slots constituting the frame, and timing storing unit which stores timing for transmitting and receiving a frame including the control channel. In the case that a traffic channel is allocated to every time slot constituting the frame, when any of the traffic channels is disconnected to make a time slot open, the control unit controls the communication unit such that the control channel is transmitted and received in the time slot which has become open in a frame transmitted and received at the timing.

[0014] In a third aspect of a cell station according to the present invention, when traffic is reduced, the cell station judges that there is call loss attributable to interference with control channels of other cell stations, and adjusts a timing for transmitting and receiving a frame including the control channel is adjusted.

[0015] For example, a cell station in this aspect of the present invention is a cell station accommodating a personal station by using a time division multiple access method, including communication unit which transmits and receives a frame including a plurality of time slots, control unit which allocates a traffic channel or a control channel to each of the time slots constituting the frame, and traffic monitoring unit which monitors communication traffic. The control unit performs carrier sensing for the control channel in a time slot to which the control channel is allocated according to results of the monitoring by the traffic monitoring unit and adjusts timing for transmitting and receiving a frame including the control channel.

[0016] In a fourth aspect of a cell station according to the present invention, the cell station automatically switches an operation mode decided before service is started according to actual traffic.

[0017] For example, a cell station in this aspect of the present invention is a cell station accommodating a personal station by using a time division multiple access method, including communication unit which transmits and receives a frame including a plurality of time slots, control unit which allocates a traffic channel or a control channel to each of the time slots constituting the frame, and traffic monitoring unit which monitors communication traffic. The control unit operates in either of a first mode in which the control channel is always allocated to at least one of the time slots constituting the frame and a second mode in which a traffic channel can be allocated to every time slot constituting the frame, and switches the operation mode according to results of the monitoring by the traffic monitoring unit.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 is a schematic diagram of a radio communication system to which an embodiment of the present invention is applied;

[0019]FIG. 2 shows an example of a format of communication frames transmitted and received between a cell station 10 and a personal station 30;

[0020]FIG. 3 is a schematic configuration diagram of the cell station 10;

[0021]FIG. 4 is a flow chart for explaining an operation of a main control section 105 performed when the cell station 10 is started up;

[0022]FIG. 5 is a flow chart for explaining a process of canceling allocation of a control channel to a time slot performed by the main control section 105 at a call connecting process;

[0023]FIG. 6 is a sequence diagram showing a flow of processes until a traffic channel is established between the cell station 10 whose operation is set in a high traffic mode and the personal station 30;

[0024]FIG. 7 is a flow chart for explaining a process of reallocating a control channel to a time slot performed by the main control section 105 at a call disconnecting process;

[0025]FIG. 8 is a flow chart for explaining a process of adjusting transmission/reception timing for a communication frame 60 carrying a control channel performed by the main control section 105; and

[0026]FIG. 9 is a flow chart for explaining an operation mode switching process performed by the main control section 105.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0027] A preferred embodiment of the present invention will now be described.

[0028]FIG. 1 is a schematic diagram of a radio communication system to which an embodiment of the present invention is applied.

[0029] For example, the radio communication system according to the present embodiment is a personal handyphone system as defined in “Second Generation Cordless Telephone System RCR STD-28” issued by Research & Development Center for Radio System, and it is used in a service area having a high traffic such as a flourishing town. As illustrated, the system is configured by connecting a plurality of cell stations 101 to 10 _(n) (hereinafter also simply referred to as cell stations 10) and a maintenance terminal 20 which monitors the states of operation of the cell stations 10 through a communication network 50 such as a PSTN (Public Switched Telephone Network)

[0030] The cell stations 10 accommodate a personal station 30 by using the time division multiple access method. A plurality of the cell station 10 forms a service area 40 in which the personal station 30 can communicate with the communication network 50. Although only one personal station 30 is shown in FIG. 1, it is obvious that there may be a plurality of personal stations 30.

[0031] For example, the personal station 30 selects a cell station 10 in a good environment for communication based on receiving condition of a control channel transmitted by each of the cell stations 10. It performs communication by transmitting and receiving communication frames to and from the selected cell station 10.

[0032]FIG. 2 shows an example of a format of communication frames transmitted and received between the cell station 10 and the personal station 30. As illustrated, the cell station 10 performs communication by sequentially transmitting and receiving communication frames 60 formed by a plurality of time slots to and from the personal station 30. A communication frame 60 has a plurality of transmission slots 601 which are transmitted from the cell station 10 to the personal station 30 and a plurality of reception frames 602 which are received by the cell station 10 from the personal station 30. The transmission slots 601 and the reception slots 602 are equal in quantity. For example, in the case of a personal handyphone system as described above, a communication frame 60 is formed by eight time slots in total, i.e., four transmission slots 601 and four reception slots 602, and it has a frame period of 5 ms.

[0033] The cell stations 10 of the present embodiment operate in either of a first mode in which a pair of a transmission slot 601 and a reception slot 602 in a communication frame 60 is always allocated to a control channel (referred to as normal mode) and a second mode in which all time slots in a communication frame 60 can be allocated to the traffic channel (referred to as high traffic mode). By way of example, FIG. 2 shows a case in which a pair of a transmission slot (a third transmission slot) 601 and a reception slot (a third reception slot) 602 in a communication frame 60 is allocated to the traffic channel. It is not essential that the traffic channel is stored in each of the communication frames 60. The control channel may be transmitted or received by storing the control channel in a predetermined transmission slot 601 and/or a predetermined reception slot 602 of communication frames 60 which are transmitted and received at an arbitrary frame period. In the example shown in FIG. 2, the frame period of a control channel transmission frame for transmission of the control channel from the cell station 10 to the personal station 30 comes at every 5n-th (n is a natural number, e.g., 20) frame.

[0034] The cell station 10 will be described in detail. An existing personal station such as a personal handyphone system that communicates with the cell station 10 by using the time division multiple access method may be used as the personal station 30. The maintenance terminal 20 is a common terminal which manages and outputs various kinds of information transmitted thereto from the cell station 10. Therefore, no detailed description is given on the personal station 30 and the maintenance terminal 20.

[0035]FIG. 3 is a schematic configuration diagram of the cell station 10.

[0036] As illustrated, the cell station 10 has a transmission system radio device 102, a reception system radio device 103, a radio control section 104, a main control section 105, a storage section 106, a channel control section 107, and an antenna 108. For example, the cell station 10 of the present embodiment is realized through the execution of a program in a memory by a CPU of an information processing apparatus which has the CPU, the memory, a communication device, and a radio communication device. In this case, the memory is used as the storage section 106.

[0037] The transmission system radio device 102 performs a predetermined modulation process on transmission slots 601 received from the radio control section 104 and transmits them from the antenna 108. The reception system radio device 103 performs a predetermined demodulation process on signals received by the antenna 108 to restore reception slots 602 and passes the reception slot 602 thus restored to the radio control section 104. The radio control section 104 transmits and receives communication frames 60 to and from the personal station 30 through the transmission system radio device 102 and the reception system radio device 103. The channel control section 107 transmits and receives communication data and control data to and from the communication network 50 according to a communication protocol adopted by the communication network 50. Various kinds of information (such as the operation mode of the cell station 10, information on whether the operation mode can be switched or not, and a threshold for operation mode switching) to be used by the main control section 105 are stored in the storage section 106. The main control section 105 controls operations of the cell station 10 as a whole.

[0038] Specifically, the main control section 105 transmits and receives call control data to and from the communication network 50 through the channel control section 108. Whereby the main control section 105 performs a call control process to establish a channel to the communication network 50. The main control section 105 also transmits and receives call control data to and from the personal station 30 through the radio control section 104 using transmission slots 601 for transmitting a control channel and reception slots 602 for receiving the control channel. Thus, a call control process is performed to allocate a traffic channel with the personal station 30 to a pair of a transmission slot 601 and a reception slot 602 of a communication frame 60 to establish a radio channel to the personal station 30. Timing for a control channel transmission frame is instructed by the main control section 105 to the radio control section 104. According to the instruction from the main control section 105, the radio control section 104 stores call control data in a predetermined transmission slot of the control channel transmission frame and transmits the control channel transmission frame by using the transmission system radio device 102. The main control section 105 also exchanges communication data transmitted and received through the channel established between the channel control section 108 and the communication network 50 and communication data transmitted and received through the radio channel established between the radio control section 104 and the personal station 30. Whereby, the personal station 30 is connected to the communication network 50. The main control section 105 also receives information on the control channel transmitted by other cell stations 10 through the reception system radio device 103.

[0039] In addition to the above-described processes, the main control section 105 performs a process for increasing the traffic that can be processed by the cell station 10 without reducing communication quality.

[0040] First, the main control section 105 decides the operation mode (either of the normal mode and high traffic mode) when the cell station 10 is started up (initial operation). FIG. 4 is a flow chart for explaining the operation of the main control section 105 performed when the cell station 10 is started up.

[0041] The main control section 105 sets an operation mode by reading operation mode identification information for the cell station 10 which has been set by an operator and stored in advance in the storage section 106 (step S101). The main control section 105 receives control channel information transmitted by other cell stations 10 located in the neighborhood of own cell station 10 through the reception system radio device 103 and the radio control section 104 and stores the information in the storage section 106 (step S102).

[0042] Next, the main control section 105 judges which of the normal mode and the high traffic mode has been set (step S103). When the normal mode has been set, the process proceeds to step S106. When the high traffic mode has been set, it is checked whether the number of cell stations 10 transmitting the control channel stored in the storage section 106 is equal to or greater than a threshold which has been set by the operator and stored in advance in the storage section 106 (step S104). When the number is equal to or greater than the threshold, the process proceeds to step S106. When the number is not equal to or greater than the threshold, the main control section 105 changes the operation mode setting from the high traffic mode to the normal mode (step S105), and then the process proceeds to step S106.

[0043] Next, at step S106, the main control section 105 reads operation mode switchability information for own cell station 10 which has been set by the operator and stored in advance in the storage section 106 and makes a setting accordingly. The main control section 105 then performs carrier sensing to determine slots to be allocated to the control channel and frame transmission/reception timing such that no interference with control channels of the other cell stations 10 occurs (step S107). Since existing techniques are used for determining slots to be allocated to a control channel and frame transmission/reception timing through carrier sensing, no detailed description will be made in this regard.

[0044] When slots to be allocated to the control channel and frame transmission/reception timing are determined as described above, the main control section 105 controls the radio control section 104 such that communication frames having control channel information stored in the allocated slots thereof are transmitted and received at the frame transmission/reception timing (step S108). Then, the operation of the cell station 10 is started.

[0045] When the flow shown in FIG. 4 terminates and the cell station 10 enters an operating state, the main control section 105 performs a process of canceling the allocation of time slots to the control channel and a process of reallocating time slots to the control channel according to the operation mode which has been set, the operation mode switchability information, and the state of occupation of time slots that constitute a communication frame 60.

[0046]FIG. 5 is a flow chart for explaining the process of canceling the allocation of time slots to the control channel that is performed by the main control section 105 at a call connecting process.

[0047] First, when a link channel establishment request is received from the personal station 30 through a communication frame 60 for transmitting and receiving the control channel (YES at step S201), the main control section 105 checks whether there is a pair of open slots (a transmission slot 601 and a reception slot 602) in the communication frame 60 transmitted and received by the radio control section 104 (step S202).

[0048] When it is found at step S202 that a pair of open slots exists, the main control section 105 allocates the traffic channel of the personal station 30 which has transmitted the link channel establishment request to the pair of open slots and performs carrier sensing in the open slots to determine the frequency of the traffic channel (step S203). The main control section 105 then performs a process of synchronizing the traffic channel between the personal station 30 which has transmitted the link channel establishment request (step S204) and own cell station 10. When the synchronization process is successful and the traffic channel is established (YES at step S205), the traffic channel synchronizing process is followed by a call control process (step S206) that is performed between the personal station 30 and own cell station 10 to establish a radio channel to the personal station 30. The process then returns to step S201. When the synchronizing process fails and the traffic channel is not established (NO at step S205), the process returns to step S201.

[0049] When there is no pair of open slots at step S202 or when a traffic channel or control channel has been allocated to every time slot constituting the communication frame 60, the main control section 105 checks whether the operation mode set for itself in the flow shown in FIG. 4 is the high traffic mode (step S207).

[0050] When it is found at step S207 that the operation mode is not the high traffic mode or when the operation mode is the normal mode, the main control section 105 increments the value in a counter which is, for example, automatically reset when a predetermined time passes to update the number of rejections of link establishment requests per the predetermined time (step S208). Then, the main control section 105 notifies the personal station 30 of the rejection of the link establishment request through the communication frame 60 for the transmission and reception of the control channel (step S209), and the process thereafter returns to step S201.

[0051] When it is found at step S207 that the operation mode is the high traffic mode, the main control section 105 performs carrier sensing in the time slots to which the control channel is allocated to retrieve frequencies for traffic channels (step S210). When the carrier sensing reveals that interference occurs at any frequency that traffic channels can use in the time slots to which the control channel is allocated and that no traffic channel can be allocated to the times lots (NO at step S211), the main control section 105 notifies the personal station 30 of there jection of time slot allocation through the communication frame 60 for transmitting and receiving the control channel (step S209), and the process thereafter returns to step S201. On the contrary, when a frequency that traffic channels can use is detected in the time slots to which the control channel is allocated as a result of the carrier sensing (YES at step S211), the main control section 105 notifies the personal station 30 of the allocation of time slots through the communication frame 60 for transmitting and receiving the control channel (step S212).

[0052] After notifying the personal station 30 of the time slot allocation, the main control section 105 stores the timing of transmission and reception of the communication frame 60 for transmitting and receiving the control channel at the radio control section 104 in the storage section 106 (step S213). Then, it waits for transmission of a re-request for link channel establishment from the personal station 30 (steps S214 and S215) for a predetermined time. The predetermined time is set such that it is longer than an estimated time until the reception of the re-request for link channel establishment when the request is sent as a response of the personal station 30 to the allocation notice and such that it is shorter than an estimated time until the reception of an up synchronization burst signal when the signal is transmitted as the response. This makes it possible to process either of a link channel establishment re-request and an up synchronization burst signal using the same time slot.

[0053] When a link channel establishment re-request is sent from the personal station 30 within the predetermined time (YES at step S214), the process returns to step S210 to continue the retrieval of frequencies for traffic channels. On the contrary, when no link channel establishment re-request is sent from the personal station 30 within the predetermined time (YES at step S215, in which case an up synchronization burst signal is sent as a response of the personal station 30 to the allocation notice), the main control section 105 causes the radio control section 104 to stop transmitting and receiving the control channel and cancels the allocation of the control channel to time slots (step S216). Then, it instructs the radio control section 104 to perform a traffic channel synchronizing process according the time slot and frequency allocated to the personal station 30 (step S217). Whereby, the radio control section 104 performs a traffic channel synchronizing process by exchanging synchronization burst signals with the personal station 30 through the transmission system radio device 102 and the reception system radio device 103.

[0054] When the synchronizing process at step S217 is successful and a traffic channel is established (YES at step S218), the main control section 105 performs a call control process with the personal station 30 to establish a radio channel (S219). On the contrary, when the synchronizing process at step S217 fails and no traffic channel is established (NO at step S218), the main control section 105 re-allocates the control channel to the time slots for which control channel allocation has been canceled (step S220). Then, the main control section 105 reads the timing for transmission and reception of the communication frame 60 for transmitting and receiving the control channel stored in the storage section 106 and causes the radio control section 104 to resume transmission and reception of the communication frame 60 for transmitting and receiving the control channel at the timing for transmission and reception (step S221).

[0055]FIG. 6 is a sequence diagram showing a flow of the process performed until a traffic channel is established between the cell station 10 whose operation mode is set to the high traffic mode and the personal station 30. It is assumed that there is no open slot in communication frames 60 transmitted and received by the cell station 10.

[0056] First, the personal station 30 transmits a link channel establishment request message to the cell station 10 (step SQ301). Upon receipt of the link channel establishment request message, the cell station 10 performs step S210 in FIG. 5 because there is no open slot in the communication frames 60 transmitted and received by itself and the high traffic mode is set as the operation mode. That is, the time slot to which the control channel is allocated is chosen as a time slot to be allocated to the traffic channel, and carrier sensing is performed in the time slot to retrieve frequencies for traffic channels (step SQ302). Then, an allocation message including specification of the allocated times lot and frequency is transmitted to the personal station 30 (step SQ303).

[0057] When the allocation message from the cell station 10 is received, the personal station 30 performs carrier sensing according to the time slot and frequency specified by the allocation message to check whether the time slot and frequency can be used as a traffic channel (SQ304). When they cannot be used because of reasons such as interference, a link channel establishment re-request message is transmitted to the cell station 10 (step SQ305).

[0058] The cell station 10 receives the link channel establishment re-request message transmitted by the personal station 30 within a predetermined time (a control channel transmission/reception duration 701) after the transmission of the allocation message in the processes at steps S214 and S215 shown in FIG. 5. The cell station 10 then performs step S210 in FIG. 5 to re-retrieve frequencies for traffic channels (step SQ306) and transmits an allocation message including specification of a time slot and a frequency to be allocated to the personal station 30 again (step SQ307) Upon receipt of the allocation message again from the cell station 10, the personal station 30 performs a process similar to step SQ304 to check whether the time slot and frequency specified by the allocation message can be used as a traffic channel (step SQ308). When they can be used, it transmits an up synchronization burst signal to the cell station 10 using the time slot and frequency (step SQ310).

[0059] Since the cell station 10 has not received the link channel establishment re-request message transmitted by the personal station 30 within the control channel transmission/reception duration 701 after the transmission of the allocation message in the processes at steps S214 and S215 shown in FIG. 5, it performs the process at step S216 in FIG. 5 to stop transmission and reception of the control channel and to cancel the allocation of the control channel to a time slot (step SQ309). Thereafter, it receives an up synchronization burst signal transmitted by the personal station 30.

[0060] In the case of the above-described personal handyphone system, the personal station 30 transmits the up synchronization burst signal before time-out of an up synchronization burst signal waiting timer (TR101C-1) 702 which is started after the transmission of the allocation message at the cell station 10. The time-out comes 100 ms after the timer is started. Upon receipt of the allocation message, the personal station 30 performs carrier sensing in four communication frames 60. Since a communication frame 60 of the above-described personal handyphone system is 5 ms, the carrier sensing is performed for 20 ms. Therefore, the timing of transmission of the link channel establishment re-request message from the personal station 30 comes at least 20 ms after the reception of the allocation message. When no allocation message is received from the cell station 10, the personal station 30 transmits another link channel establishment request message again 1200 ms after the transmission of the message requesting link channel establishment request message. This process is repeated up to three times.

[0061] Therefore, in the case of the personal handyphone system described above, the control channel transmission/reception duration 701 is set taking those points into consideration. Specifically, the duration is to start 1200 ms after the transmission of a link establishment request message and to end within a time range between 20 ms and 100 ms after the transmission of an allocation message. The duration is to be longer than an estimated time until the reception of a re-request for link channel establishment re-request message at the cell station 10 when the link channel establishment re-request message is sent as a response of the personal station 30 to the allocation message. The duration is to be shorter than an estimated time until the reception of an up synchronization burst signal at the cell station 10 when the up synchronization burst signal is transmitted as the response of the personal station 30 to the allocation message.

[0062] When the cell station 10 receives the up synchronization burst signal before the time-out of the up synchronization burst signal waiting timer 702, it transmits a down synchronization burst signal to the personal station 30 (step SQ311). When the personal station 30 receives the down synchronization burst signal before time-out of a down synchronization burst signal waiting timer (TR101P-1) 703 which is started after the transmission of the up synchronization burst signal (the time out comes 100 ms after the timer is started), it transmits a TCH (traffic channel) idle burst signal to the cell station 10 (step SQ312). When the cell station 10 receives the TCH idle burst signal before time-out of a TCH idle burst signal waiting timer (TR101C-2) 704 which is started after the transmission of the down synchronization burst signal, it transmits a TCH idle burst signal to the personal station 30 (step SQ313). When the personal station 30 receives the TCH idle burst signal before time-out of a TCH idle burst signal waiting timer (TR101P-2) 705 which is started after the transmission of the TCH idle burst signal, a traffic channel is established (step SQ314).

[0063]FIG. 7 is a flow chart for explaining a process of reallocating the control channel to a time slot that is performed by the main control section 105 at a call disconnect process.

[0064] When the radio control section 104 receives a call disconnect message from a certain personal station 30 through a traffic channel, the main control section 105 transmits the call disconnect message to the communication network 50 through the channel control section 107 and cancels the allocation of the traffic channel to a time slot is cancelled. When the cancellation of the allocation of the traffic channel to a time slot results in any open slot in communication frames 60 transmitted and received by the radio control section 104 through the transmission system radio device 102 and the reception system radio device 103 (YES at step S401), the main control section 105 checks whether the operation mode set for itself is the high traffic mode (step S402). When the operation mode is the high traffic mode, the main control section 105 further checks whether the transmission and reception of the control channel is currently stopped by the radio control section 104 (step S403).

[0065] When the transmission and reception of the control channel is stopped by the radio control section 104 (YES at step S403), the main control section 105 reads the timing of transmission and reception of a communication frame 60 carrying the control channel stored in the storage section 106 (step S404) Next, the main control section 105 performs carrier sensing for the control channel in the newly generated open slot at the read transmission/reception timing of the communication frame 60 to check whether there is any interference with the control channel (step S405).

[0066] When it is found that there is interference with the control channel as a result of the carrier sensing (YES at step S406), the main control section 105 transmits, through any of the traffic channels, a message to the personal station 30 that is communicating using this traffic channel to notify the personal station 30 that the time slot to which the traffic channel is allocated will be changed to the open slot (a TCH switch message in the case of the above-described personal handyphone system). Whereby, the time slot to which the traffic channel has been allocated is changed to the open slot (step S407). The process then returns to step S405 at which the main control section 105 performs carrier sensing for the control channel in the newly generated open slot at the transmission/reception timing for the communication frame 60 for transmitting and receiving the control channel read as described above.

[0067] When it is found that there is no interference with the control channel as a result of the carrier sensing (NO at step S406), the main control section 105 allocates the control channel to the open slot (step S408). Then, it causes the radio control section 104 to resume the transmission and reception of the communication frame 60 for transmitting and receiving the control channel at the transmission/reception timing for the communication frame 60 for transmitting and receiving the control channel read from the storage section 106 (step S409).

[0068] When the flow shown in FIG. 4 is terminated and the cell station 10 enters the operating state, the main control section 105 monitors the state of communication traffic. According to results of the monitoring, it performs a process of adjusting the transmission/reception timing of the communication frame 60 carrying the control channel and a process of switching the operation modes.

[0069]FIG. 8 is a flow chart for explaining the process of adjusting the transmission/reception timing of the communication frame 60 carrying the control channel performed by the main control section 105.

[0070] While the radio control section 104 transmits and receives the control channel, the main control section 105 counts the number of link channel establishment requests received by the radio control section 104 through the control channel within a predetermined time (e.g., one hour) (steps S501, S502, and S503). It is judged whether the count value is equal to or smaller than a predetermined threshold (referred to as adjustment reference value) stored in the storage section 106 (step S504). For example, the adjustment reference value is set at the number (an estimated value) of received link channel establishment requests in a case wherein it seems that proper transmission and reception of the control channel is not performed because of interference.

[0071] When the count value within the predetermined time is equal to or smaller than the adjustment reference value (YES at step S504), the main control section 105 causes the radio control section 104 to suspend the transmission and reception of the control channel (step S505). Then the main control section 105 performs carrier sensing to decide again a slot to be allocated to the control channel and frame transmission/reception timing at which no interference with the control channels of other cell stations 10 occurs (step S506). The radio control section 104 is then caused to resume the transmission and reception of the communication frame 60 for transmitting and receiving the control channel at the slot and frame transmission/reception timing thus decided again (step S507).

[0072] When the radio control section 104 stops transmitting and receiving the control channel (NO at step S501), the count value is cleared (step S508).

[0073] In the flow shown in FIG. 8, the transmission/reception timing for the communication frame 60 carrying the control channel is re-decided each time a predetermined time passes during the transmission and reception of the control channel based on a value counted within the predetermined time. For example, values counted within the predetermined time may be stored in the storage section 106; an average of such count values may be obtained when the number of the count values reaches a predetermined number (e.g., when the number of the count values is counted for a day); and the processes at steps S504 to S507 may be performed on the average value thus obtained.

[0074]FIG. 9 is a flow chart for explaining the operation mode switching process performed by the main control section 105.

[0075] The main control section 105 counts the number of allocation reject messages in response to link channel establishment requests transmitted by the radio control section 104 within a predetermined time (e.g., one hour) (steps S601 and S602). Then, the main control section 105 judges whether the count value is equal to or greater than a predetermined threshold (referred to as reference value for switching to the high traffic mode) stored in the storage section 106 (step S603). The reference value for switching to the high traffic mode is set at the number (an estimated value) of allocation reject messages transmitted in a case wherein it seems that possibility of rejection of a link channel establishment request is higher because of an increase in the traffic.

[0076] When the count value within the predetermined time is equal to or greater than the reference value for switching to the high traffic mode (YES at step S603), the main control section 105 checks whether the operation mode switchability information read at step S106 in FIG. 4 indicates that operation mode switching is enabled (step S604). If the information indicates that operation mode switching is enabled, the main control section 105 further checks whether the operation mode set for own cell station 10 is the normal mode (step S605). When the operation mode set for own cell station 10 is the normal mode (YES at step S605), the main control section 105 changes the operation mode from the normal mode to the high traffic mode (step S606). The process thereafter proceeds to step S611. When the operation mode switchability information indicates that operation mode switching is disabled (NO at step S604) or when the operation mode set for own cell station 10 is the high traffic mode (NO at step S605), the process proceeds to step S611 without changing the operation mode.

[0077] When the count value within the predetermined time is not equal to or greater than the reference value for switching to the high traffic mode (NO at step S603), the main control section 105 judges whether the count value is equal to or smaller than a predetermined threshold (referred to as reference value for switching to the normal mode) stored in the storage section 106 (step S607). The reference value for switching to the normal mode is set at the number (an estimated value) of allocation reject messages transmitted in a case wherein it seems that possibility of rejection of a link channel establishment request is lower because of a reduction in the traffic.

[0078] When the count value within the predetermined time is not equal to or smaller than the reference value for switching to the normal mode (NO at step S607), the process returns to step S601. When the count value is equal to or smaller than the reference value for switching to the normal mode (YES at step S607), the main control section 105 checks whether the operation mode switchability information indicates that operation mode switching is enabled (step S608). If the information indicates that operation mode switching is enabled, the main control section 105 further checks whether the operation mode set for own cell station 10 is the high traffic mode (step S609). When the operation mode set for own cell station 10 is the high traffic mode (YES at step S609), the main control section 105 changes the operation mode from the high traffic mode to the normal mode (step S610). The process thereafter proceeds to step S611. When the operation mode switchability information indicates that operation mode switching is disabled (NO at step S608) or when the operation mode set for own cell station 10 is the normal mode (NO at step S609), the process proceeds to step S611 without changing the operation mode.

[0079] At step S611, the main control section 105 controls the channel control section 107 to transmit the operation mode set for own cell station 10, the operation mode switchability information, and the state of communication traffic (the number of allocation reject messages within the predetermined time) to the maintenance terminal 20 through the communication network 50. Then, the count value is cleared (step S612), and the process returns to step S601. Upon receipt of the above information, the maintenance terminal 20 notifies maintenance personnel of the operation mode, the operation mode switchability information, and the state of communication traffic notified by the cell station 10 by displaying them on a display. This allows the maintenance personnel to judge the state of service in the current operation mode and to reconsider the installation place, the operation mode and operation mode switchability information of own cell station 10.

[0080] In the flow shown in FIG. 9, whether to switch the operation mode is judged each time a predetermined time passes based on a value counted within the predetermined time. For example, values counted within the predetermined time may be stored in the storage section 106; an average of such count values may be obtained when the number of the count values reaches a predetermined number (e.g., when the number of the count values is counted for a day); and the processes at steps S603 to S611 may be performed on the average value thus obtained.

[0081] A preferred embodiment of the invention has been described above.

[0082] In the embodiment, when the radio control section 104 receives a link channel establishment request message from the personal station 30 through the control channel that is allocated to any time slot in a state in which a channel is allocated to every time slot constituting a communication frame 60, the main control section 105 notifies the personal station 30 of an allocation message through the control channel to indicate that the time slot allocated to the control channel will be allocated to a traffic channel. The transmission of the control channel is stopped when a predetermined time (the control channel transmission/reception duration 701) passes after the notification of the allocation message. Therefore, in the present embodiment, in a case wherein the time slot for the control channel is allocated to the traffic channel of a certain personal station 30 and the personal station 30 cannot recognize a traffic channel thus allocated, a re-request for allocation transmitted by the personal station 30 can be received. It is therefore possible to suppress any reduction in connectability of a call from the personal station 30.

[0083] In the present embodiment, in a case wherein a traffic channel is allocated to every time slot constituting a communication frame 60 and any of the traffic channels is disconnected to produce an open slot, the main control section 105 controls the radio control section 104 such that a control channel is transmitted and received in the open slot in the communication frame 60 that is transmitted and received at frame transmission/reception timing stored in the storage section 106. The frame transmission/reception timing is transmission/reception timing of the communication frame 60 of a control channel in which no interference has been detected during carrier sensing and which has been properly transmitted and received. Therefore, the possibility of detection of interference is reduced by performing carrier sensing in the control channel at that transmission/reception timing, and the possibility of successful allocation of the control channel to the open slot is thus increased.

[0084] Even if interference is detected, in the present embodiment, the open slot is changed to a slot to which a traffic channel is allocated, and another time slot is made open and is subjected to carrier sensing for the control channel. Since the control channel can be thus allocated to any time slot, the occurrence of call loss and a resultant reduction of traffic can be prevented.

[0085] In the present embodiment, the main control section 105 monitors the number of link channel establishment request messages received within a predetermined time. When the number of received requests is equal to or smaller than a predetermined adjustment reference value, carrier sensing for the control channel is performed in the time slot to which the control channel is allocated to adjust the timing for transmitting and receiving the frame including the control channel. This makes it possible to prevent proper transmission and reception of the control channel from being disabled by interference, and the occurrence of call loss and a resultant reduction in traffic can be prevented.

[0086] In the present embodiment, the main control section 105 monitors the number of link channel establishment request messages transmitted within a predetermined time and controls the switching of operation modes according to results of the monitoring. Specifically, the operation mode is switched from the normal mode to the high traffic mode when the number of transmitted messages is equal to or greater than a predetermined reference value for switching to the high traffic mode, and the operation mode is switched from the high traffic mode to the normal mode when the number of transmitted messages is equal to or smaller than a predetermined reference value for switching to the normal mode (provided that operation mode switchability information indicates that switching is enabled). This allows an operation mode decided before the starting of the service to be automatically switched to another according to actual traffic.

[0087] The present embodiment thus makes it possible to increase traffic that can be processed at a cell station without reducing communication quality.

[0088] The invention is not limited to the above-described embodiment and may be modified in various ways within the scope of the teaching thereof. For example, the above-described functions of the cell station 10 are not limited to implementation on a software basis through execution of a program in a memory by a CPU in an information processing apparatus having a CPU, a memory, and a communication device. Alternatively, the functions may be provided on a hardware basis using an integrated circuit such as an ASIC.

[0089] As described above, the invention makes it possible to increase traffic that can be processed by a cell station without reducing communication quality. 

What is claimed is:
 1. A cell station accommodating a personal station by using a time division multiple access method, comprising: communication unit which transmits and receives a frame including a plurality of time slots; and control unit which allocates a traffic channel or a control channel to each of the time slots constituting the frame, wherein, in the case that a channel is allocated to every time slot constituting the frame and the communication unit receives a link channel establishment request from the personal station through the control channel allocated to any of the time slots, the control unit notifies the personal station through the control channel that the time slot allocated to the control channel will be allocated to a traffic channel and stops transmission and reception of the control channel when a predetermined time passes after the notice.
 2. A cell station according to claim 1, wherein the predetermined time is set such that it is longer than an estimated time until the reception of a link channel establishment re-request when the re-request is sent as a response of the personal station to the notice and is shorter than an estimated time until the reception of a synchronization burst signal when the signal is set as the response.
 3. A cell station accommodating a personal station by using a time division multiple access method, comprising: communication unit which transmits and receives a frame including a plurality of time slots; control unit which allocates a traffic channel or a control channel to each of the time slots constituting the frame; and timing storing unit which stores timing for transmitting and receiving a frame including the control channel, wherein, in the case that a traffic channel is allocated to every time slot constituting the frame, when any of the traffic channels is disconnected to make a time slot open, the control unit controls the communication unit such that the control channel is transmitted and received in the time slot which has become open in a frame transmitted at said timing.
 4. A cell station according to claim 3, wherein: the control unit controls the communication unit to perform carrier sensing for the control channel in the time slot which has become open in the frame transmitted and received at said timing; when no interference is detected, the control unit controls the communication unit to transmit and receive the control channel in the time slot which has become open in the frame transmitted and received at said timing; and when interference is detected, the control unit controls the communication unit such that it repeats a process of switching a traffic channel allocated to another time slot to the time slot which has become open and performing carrier sensing for the control channel in the another time slot in a frame transmitted and received at timing stored in the timing storing unit until no interference is detected and it transmits and receives the control channel in a time slot in which no interference has been detected in the frame transmitted and received at said timing.
 5. A cell station accommodating a personal station by using a time division multiple access method, comprising: communication unit which transmits and receives a frame including a plurality of time slots; control unit which allocates a traffic channel or a control channel to each of the time slots constituting the frame; and traffic monitoring unit which monitors communication traffic, wherein the control unit performs carrier sensing for the control channel in a time slot to which the control channel is allocated according to results of the monitoring by the traffic monitoring unit and adjusts timing for transmitting and receiving a frame including the control channel.
 6. A cell station according to claim 5, wherein: the traffic monitoring unit monitors the number of link channel establishment requests received from the personal station through the control channel within a predetermined time as the communication traffic; and the control unit performs said adjustment when the communication traffic monitored by the traffic monitoring unit is equal to or smaller than a predetermined threshold.
 7. A cell station accommodating a personal station by using a time division multiple access method, comprising: communication unit which transmits and receives a frame including a plurality of time slots; control unit which allocates a traffic channel or a control channel to each of the time slots constituting the frame; and traffic monitoring unit which monitors communication traffic, wherein: the control unit operates in either of a first mode in which the control channel is always allocated to at least one of the time slots constituting the frame and a second mode in which a traffic channel can be allocated to every time slot constituting the frame; and the operation modes are switched according to results of the monitoring by the traffic monitoring unit.
 8. A cell station according to claim 7, wherein: the traffic monitoring unit monitors the number of rejections of link channel establishment requests received from the personal station through the control channel within a predetermined time as the communication traffic; and the control unit switches the operation mode to the second mode when the communication traffic monitored by the traffic monitoring unit becomes equal to or greater than a predetermined threshold during an operation in the first mode.
 9. A radio communication system having a plurality of cell stations and a communication network connecting the plurality of cell stations, wherein at least one of the plurality of cell stations is a cell station according to claims
 1. 10. A communication control method for a cell station accommodating a personal station by using a time division multiple access method, wherein: in the case that a channel is allocated to every time slot constituting the frame, when a link channel establishment request is received from the personal station through the control channel allocated to any of the time slots, the personal station is notified through the control channel that the time slot allocated to the control channel will be allocated to a traffic channel; and transmission and reception of the control channel is stopped when a predetermined time passes after the notice.
 11. A communication control method for a cell station accommodating a personal station by using a time division multiple access method, wherein, in the case that a traffic channel is allocated to every time slot constituting the frame, when any of the traffic channels is disconnected to make a time slot open, the control channel is transmitted and received in the time slot which has become open in a frame transmitted and received at timing stored in advance in storing unit.
 12. A communication control method for a cell station accommodating a personal station by using a time division multiple access method, comprising the steps of: monitoring communication traffic; and performing carrier sensing for a control channel in a time slot to which the control channel is allocated and adjusting timing for transmitting and receiving a frame including the control channel when results of the monitoring becomes equal to or greater than a predetermined threshold.
 13. A communication control method for a cell station accommodating a personal station by using a time division multiple access method, comprising the steps of: monitoring communication traffic; and switching the operation mode to a second mode in which a traffic channel can be allocated to every time slot constituting a frame when results of the monitoring becomes equal to or greater than a predetermined threshold during an operation in a first mode in which a control channel is always allocated to at least one of time slots constituting a frame to be transmitted and received.
 14. A method of constructing a radio communication network utilizing a plurality of cell stations connected to each other through a communication network, wherein at least one of the plurality of cell stations carries out the communication control method for a cell station according to claim
 10. 15. A method of constructing a radio communication network utilizing a plurality of cell stations connected to each other through a communication network, wherein at least one of the plurality of cell stations carries out the communication control method for a cell station according to claim
 11. 16. A method of constructing a radio communication network utilizing a plurality of cell stations connected to each other through a communication network, wherein at least one of the plurality of cell stations carries out the communication control method for a cell station according to claim
 12. 17. A method of constructing a radio communication network utilizing a plurality of cell stations connected to each other through a communication network, wherein at least one of the plurality of cell stations carries out the communication control method for a cell station according to claim
 13. 